DEVELOPMENT OF THE APPAI.ACHIAX GEOSYNCLINE 171 



toward the borderlands and thin ont over the neutral area or the nucleus 

 of the continent. In the east is the smaller Appalachian geosyncline, 

 and in the western part of the continent the greater Cordilleran geosyn- 

 cline. The latter finally evolves into the Rocky Mountain and Pacific 

 Sequent geosynclines of Mesozoic times. To the east of the Appalachian 

 geosyncline in greater Acadia is the small Acadian geosyncline. Finally, 

 there is in the Arctic region, on the inner side of the borderland Pearya, 

 the Franklinian geosyncline. 



EMBAY ME XT S 



Besides these geosynclines, but in connection with them, there is in the 

 .southern part of the continent the Ouachita emhayment, uniting with 

 the Appalachian geosyncline, while the southern end of the Cordilleran 

 geosyncline has the Sonoran emhayment, extending transversely across 

 Nevada, New Mexico, Texas, and Sonora (see map, figure 3). 



GREATER APPALACHIAN GEOSYXCLINE 



The Appalachian geosyncline, in the widest sense, extends from the 

 southeastern corner of Labrador and northern Newfoundland along the 

 western side of Acadia and Appalachia into the Gulf of Mexico. At the 

 northeast it appears to have been continuous wdth what is now the North 

 Atlantic, but during the Paleozoic, with Poseidon, an ocean to the north 

 of the transverse equatorial land Gondwana. At the southwest the trough 

 appears to have continued unbroken into the Gulf of Mexico and across 

 Tehuantepec into the Pacific Ocean. 



As previously stated, the Appalachian trough was in existence early in 

 Proterozoic time. Beginning with the Lower Cambrian, it appears 

 ■earliest in Alabama, Georgia, and Tennessee, and long before the close of 

 this epoch the trough was continuous from the Gulf of Mexico northeast 

 to Newfoundland. The deposits of Cambrian time are much the thickest 

 in the southern part of the trough and are from Appalachia, then a 

 mountainous land. On the other hand, in the northeastern part of the 

 geosyncline the sediments are much thinner. It should be said that in 

 the main the elastics throughout the greater Appalachian trough came 

 from the east and southeast. In all of this we see that the isostatic rela- 

 tions of the sinking geosyncline to the rising eastern lands were reestab- 

 lished during the crustal movements taking place toward or at the close 

 of Proterozoic time. 



Thus far we have spoken of the greater Appalachian geosyncline as a 

 continuous trough, and so it is from the structural viewpoint; but from 

 the local sedimentary histories it is plain that there are here combined 



